I'd argue for the usefulness at this point.
I'd say that the onus for the storage of the data is on the developer. I don't *have* to use pluginPrefs to store the value in the clear (it could be cleared out and subsequently stored in the keychain, or hashed before storage).
In my use case, I'm allowing the user to configure a password that'll be used to remotely view cameras. Sure, someone who's fairly familiar with the workings of Indigo could find out what that password is (if it were put in pluginPrefs), but the casual user "clicking through" won't be able to see it.
What I'll actually end up doing, to stop my friends who'll be beta testing for me being able to view my cameras (!), is clearing the field on validate and storing it in a non-UI element. This will, IMHO, lead to a bad user experience as there'll be no way to tell if a password is set or not.
If it were secured, I could *actually* MD5 hash the password on validate, and save it in that format. When the user authenticates with their client, I'll hash that password before transmitting it (there's no SSL here), and validate against the hash...
Anywho - if we could move it up a little, it's of value
-A